Field of the Invention
Embodiments disclosed herein generally relate to pyrometry in rapid thermal processing chambers.
Description of the Related Art
Rapid thermal processing (RTP) and epitaxial deposition (Epi) systems are employed in semiconductor chip fabrication to create, chemically alter or etch surface structures on semiconductor wafers. RTP and Epi typically depend upon an array of high-intensity incandescent lamps fit into a lamphead and directed at the substrate or wafer. The lamps are electrically powered and can be very quickly turned off and on and a substantial fraction of their radiation can be directed to the substrate. As a result, the wafer can be very quickly heated without substantially heating the chamber and can be nearly as quickly cooled once the power is removed from the lamps.
A number of infrared lamps are located in the lamphead. During processing, radiation from the lamps radiates through an upper window, light passageways and a lower window onto a rotating semiconductor substrate in the processing chamber. In this manner, the wafer is heated to a required processing temperature. The lamphead may include a number of light pipes to deliver highly collimated radiation from tungsten-halogen lamps to the processing chamber. The lamps are divided into multiple zones, which are located in a radially symmetrical manner. Each zone is separately powered by a lamp driver that is, in turn, controlled by a multi-input, multi-output controller. The lamps are connected to the lamp drivers through a large wiring collar and heavy-duty electrical cabling.
During a heating process, the heated substrate releases radiation which is received by one or more pyrometers. The radiation received is used to determine the temperature of the substrate. However, it is believed that other radiation sources, such as the lamps, produce noise which distorts the detected radiation at the pyrometer. This noise combines with the radiation from the substrate to create a combination photocurrent which represents the detection of both the heat and the noise at the pyrometer. One approach to address the problem is to mechanically or optically shield or block stray radiation to the pyrometers using shield rings or spectrally selective windows or lenses. However, mechanical shielding or blocking can be insufficient to prevent noise while allowing proper radiation to pass. Further, for some applications that require the pyrometer to be on the same side as the lamphead, such shielding approaches are not feasible.
Thus, there is a need in the art for correction of noise detected at a pyrometer during thermal processing.